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Off-the-rails thinking saves time and costs for Carillion

Southampton to Basingstoke gauge clearance project was delivered thanks to prefab and precast approaches to programme-critical elements.

Enabling larger 9 ft, 6 inch containers to be transported by rail between Southampton docks and freight terminals in the Midlands and North required major work on the rail network between Southampton and the West Coast Main Line.

This saw Carillion carry out many significant elements of the wider Southampton to Basingstoke gauge clearance project.

The initial part was a contract to clear the main line route via the Southampton Tunnel, before moving on to the opening of the diversionary route via Salisbury.

167-year-old tunnel challenge

The scale of the challenge at Southampton Tunnel was substantial and required a number of innovative solutions.

The 483 m tunnel dates back to 1847 and has suffered from geological problems since its original opening.

It is also on the main rail route from London to Dorset and handles 20 trains an hour.

“Key to success of the larger scale track renewal work was prefabricating track panels off site and placing these in the tunnel”

To complete the gauge clearance at Southampton, it was necessary to replace the existing ballasted track with slab track.

This was to both achieve the correct clearances and, critically, prevent the tracks moving to put the running lines ‘out of gauge’. Slab tracking essentially casts the track and sleepers into concrete (at 1 mm accuracy).

Prefab panels help halve programme

Vital to success of the larger-scale track renewal work was prefabricating track panels offsite and placing these in the tunnel.

The original methodology proposed involved placing individual sleepers in the tunnel, delivered by road and shuffled into the tunnel by fork truck.

Initially it was thought the project would take two years and involve disruption to services over two Christmas holiday periods.

However, Carillion’s early involvement with Network Rail and other stakeholders enabled the project to be delivered in one year.

“The combination of cost-effective construction methods reduced possession costs, meaning less time on site”

This dramatically reduced the disruption, with a closure period of just 10 days over one Christmas.

By using single-line working through the tunnel around this 10-day period, services were maintained while work was undertaken on the adjacent line.

The combination of cost-effective construction methods reduced possession costs, meaning less time on site, which delivered savings of £13m that were allocated to gauge clearing the diversionary route via Salisbury.

Precast bridge cladding saves weeks

Carillion was awarded the bridgeworks element of this project and delivered a number of innovative design solutions. These included the brick cladding to the precast concrete Conarch Bridge structures.

Bridges on the route that would foul higher containers were renewed using the standard design and were to be clad with brickwork when installed.

However, the team realised this programme-critical element was vulnerable to bad weather and involved working at height, with the associated risks.

To circumvent this, it developed an alternative method involving cladding the concrete with brickwork in a precast facility. This saved four weeks onsite work for each bridge, as well as reducing costs.

Overall this programme delivered works that met the needs of the rail operators, local road users and other stakeholders and achieved savings of £5.6m.

The project has also won the Driving Efficiencies prize at this year’s Network Rail Partnership Awards.

Phil Bowcock is project director at Carillion

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